1. Field
Example embodiments of the following disclosure relate to a balance control apparatus of a robot which controls driving of joint units provided on a plurality of legs to keep the balance of the robot, and a control method thereof.
2. Description of the Related Art
In general, robots have a joint system similar to humans and perform motions similar to those of human hands and feet using such a joint system.
Industrial robots for automation and unmanned operation of production in factories were developed at the initial stage, however, service robots to provide various services to humans have been vigorously developed recently.
These service robots provide services to humans while walking in a manner similar to the way humans walk. Therefore, development and research into robots walking while maintaining a stable pose have been actively progressing.
As methods to control the walking of robots, there is a position-based Zero Moment Point (hereinafter, referred to as ZMP) control method, in which target positions of robot joints are tracked. In addition, there are a torque-based dynamic walking control method and a Finite State Machine (hereinafter, referred to as FSM) control method, in which target torques of robot joints are tracked.
The position-based ZMP control method achieves precise position control, but requires precise angle control of respective joints of a robot, and thus, requires high servo gain. As such, the ZMP control method requires high current, and thus, has low energy efficiency and high stiffness of the joints and may apply high impact during collusion with surrounding environments.
Further, in order to calculate angles of the respective joints through inverse kinematics from a given center of gravity (COG) and the walking patterns of the legs, the ZMP control method needs to avoid kinematic singularities, thus causing the robot to bend knees at any time during walking and to have an unnatural gait, which is different from that of a human.
Further, when inverse kinematics is used, position control of joints is needed. Here, in order to perform a desired motion, high gain is used, thus causing the joints not to flexibly cope with a temporary disturbance.
The torque-based dynamic walking control method needs to solve a dynamic equation to achieve the stable walking of a robot. However, if a robot having legs with 6 degrees of freedom moving in a random direction in a space is used, the dynamic equation becomes excessively complicated. Therefore, the dynamic equation has been applied to robots having legs with 4 degrees of freedom or less.
The FSM control method achieves control through torque commands and is applicable to an elastic mechanism, and thus, has high energy efficiency and low stiffness of joints, thereby being safe in surrounding environments. However, the FSM control method does not achieve precise position control, and thus, it is not easy to perform a precise whole body motion, such as ascending a stairway or avoiding an obstacle.